Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.57	8.410%	$59.1593	$59.16	$59.15	$59.20
Purchase #2	$34.35	10.633%	$38.0024	$38.00	$38.00	$38.00
Purchase #3	$157.85	7.584%	$169.8213	$169.82	$169.80	$169.80
Purchase #4	$54.39	8.499%	$59.0126	$59.01	$59.00	$59.00
Purchase #5	$26.59	7.640%	$28.6215	$28.62	$28.60	$28.60
Purchase #6	$114.84	4.665%	$120.1973	$120.20	$120.20	$120.20
Purchase #7	$139.72	13.828%	$159.0405	$159.04	$159.05	$159.00
7 purchase totals =	$582.31		$633.8549	$633.85	$633.80	$633.80